The disclosure of Japanese Patent Application No. 2001-020207 filed on Jan. 29, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates generally to a vibration-damping device which exhibits a vibration damping or isolating effect on the basis of an elastic deformation of a rubber elastic body, and more particularly to such a vibration-damping device which is novel in construction and which is suitably applicable to an engine mount, a body mount, and a suspension bushing for an automotive vehicle, for example.
2. Description of the Related Art
As one kind of vibration dampers such as an engine mount or a suspension bushing for an automotive vehicle, for flexibly connecting two members in a vibration system or mounting one of the two members on the other member in a vibration damping fashion, there is known a vibration-damping device having an elastic body made of rubber, which elastically connects a first and a second mounting member that are disposed in a mutually spaced-apart relationship with each other and attachable to these two members of the vibration system. Keeping pace with a recent demand on upgrading damping capability of the vibration dampers, a fluid-filled vibration-damping device has been developed. The fluid-filled vibration-damping device includes a fluid chamber partially defined by the elastic body and filled with a non-compressible fluid, and exhibits an improved vibration-damping device on the basis of resonance or flows of the non-compressible fluid in the fluid chamber induced when the vibration-damping device is subjected to a vibrational load.
Upon application of the vibrational load to such a vibration-damping device, the elastic body is elastically deformed periodically. Since the elastic body itself constitutes a vibration system, the elastic body is likely to suffer from a surging thereof upon application of the vibrational load whose frequency band corresponds to a natural frequency of the elastic body. The surging of the elastic body may deteriorate vibration damping characteristics of the vibration-damping device, whereby the vibration-damping device is incapable of exhibiting a desired damping effect.
A surging frequency: fn of the elastic body may be obtained according to the following equation on the basis of a basic model of the vibration-damping device including the first and second mounting members and the elastic body elastically connecting the first and second mounting members:
fn=(N/2L){square root over ( )}(G/xcfx81) 
where,
L: distance of effective free length of the elastic body;
G: dynamic modulus of elasticity;
xcfx81: density of the elastic body; and
N: degree of a mode of vibration.
In general, the surging of the elastic body in a first mode or harmonic of vibration (N=1) is required to be damped, since an amplitude of the surging of the elastic body is maximized in the first mode.
To cope with the problem of surging of the elastic body, various kinds of surging limiting members incorporated in the vibration-damping device has been proposed. For instance, JP-A-2-256933 discloses a surging limiting member of dynamic damper type in which a pair of support arm protrude from the elastic body so as to support mass members at their protruding end portions, respectively. These support arms and the mass members cooperate to constitute a dynamic damper serving as a subsidiary vibration system, so that the vibration-damping device equipped with this surging limiting member enables to limit or restrict the surging of the elastic body owing to resonance of the subsidiary vibration system. Further, JP-A-10-267069 discloses a surging limiting member of mass damper type in which a ring member serving as a mass damper is fixedly disposed in the elastic body so as to adjust the mass of a surging portion of the elastic body.
However, the disclosed surging members of the dynamic damper type and the mass damper type exhibit their surging limiting effects with respect only to very limited frequency bands, to which these surging members are tuned. This makes it difficult to desirably tune a natural frequency of the subsidiary vibration system, i.e., the dynamic damper of the vibration-damping device, and a natural frequency of a primary vibration system of the vibration-damping device equipped with the mass damper in the form of the ring member.
Moreover, the surging frequency of the elastic body of the vibration-damping device varies depending upon a spring stiffness of the elastic body which is changed due to a change of the ambient temperature. Therefore, even if the disclosed vibration-damping device having the surging limiting members are desirably tuned in their initial or static states, the surging limiting member may possibly become incapable of exhibiting intended surging limiting effects, due to the above-indicted change of the surging frequency of the elastic body. Thus, the conventional vibration-damping devices equipped with the surging limiting members still suffer from difficulty in exhibiting desired surging limiting effects with high stability.
It is therefore one object of this invention to provide a vibration-damping device, which is novel and simple in construction, which is able to eliminate or minimize a problem of deterioration of vibration damping capability thereof due to a surging of an elastic body thereof, and which is capable of exhibiting an excellent vibration damping effect over a wide frequency band.
The above and/or optional objects of this invention may be attained according to at least one of the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to those modes of the invention and combinations of the technical features, but may otherwise be recognized based on the thought of the present invention that disclosed in the whose specification and drawings or that may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
(1) A vibration-damping device for elastically connecting two members of a vibration system in a vibration damping fashion, the vibration-damping device comprising: (a) a first mounting member attachable to one of the two members of the vibration system; (b) a second mounting member disposed away from the first mounting member and attachable to an other one of the two members of the vibration system; (c) an elastic body disposed between and elastically connecting the first and second mounting members, the elastic body including a connecting portion that extends between the first and second mounting members and has a hollow housing portion; and (d) an independent mass member accommodated in the housing portion such that the independent mass member is independently displaceable relative to the housing portion without being bonded to the housing portion, and such that the independent mass member is brought into direct and elastic impact against the housing portion.
In the vibration-damping device constructed according to the mode (1) of the invention, the independent mass member is displaced relative to the housing portion when a vibrational load is applied between the first and second mounting members and the elastic body undergoes elastic deformation or displacement thereof. In particular, upon application of a specific vibrational load whose frequency corresponds to a surging frequency of the elastic body, an amount of the elastic deformation or displacement of the elastic body increases, resulting in an increase in an amount of displacement of the independent mass member relative to the housing portion of the connecting portion of the elastic body. This effectively induces bouncing displacement of the independent mass member relative to the housing portion, whereby the independent mass member is brought into direct and elastic impact against the housing portion, repeatedly. This impact (abutting contact) of the independent mass member against the housing portion exhibits a vibration damping effect with respect to the elastic body, thereby attenuating an amount of vibration or oscillation of the elastic body. Accordingly, the vibration-damping device of this mode permits eliminating or reducing a problem of deterioration of its vibration damping capability (i.e., an increase of a ratio of vibration transmission) due to the surging of the elastic body, thus ensuring an excellent vibration damping capability thereof with respect to various kinds of vibrations over a wide frequency range with high stability. It should be appreciated that the term xe2x80x9cconnecting portionxe2x80x9d should be interpreted to mean a part of the elastic body that extends between the first and second mounting members and is elastically deformed upon application of a vibrational load between the first and second mounting members.
The independent mass member is preferably made of a metallic material having a higher gravity. Alternatively, the independent mass member may possibly be made of a non-metallic material such as a rubber elastic body, a synthetic resin material and a foamed body of a rubber material or a synthetic resin material. It is possible to reinforce such a independent mass member made of the non-metallic material by fixing thereto a rigid member made of metal or the like.
It is noted that the vibration-damping device of this mode has no member to elastically connect the independent mass member and the housing portion with each other. Namely, an outer surface of the independent mass member is completely separated from an inner surface of the housing portion. With the independent mass member placed in a center of displacement thereof relative to the housing portion, the outer circumferential surface of the independent mass member and the inner circumferential surface of the housing portion are opposed to each other with a given spacing therebetween. Thus, the independent mass member is independently displaceable relative to the housing portion without being bonded to the housing portion.
(2) A vibration-damping device according to the above-indicated mode (1), wherein the housing portion formed in the connecting portion of the elastic body is located at a substantially central portion between the first mounting member and said second mounting member, in a direction in which the first and second mounting member are connected to each other via the connecting portion. The vibration-damping device of this mode of the invention, the housing portion is formed at the central portion of the connecting portion which corresponds to a loop of the first harmonic of the surging of the connecting portion of the elastic body, that is, the substantially central portion between the connecting ends of the connecting portion with respect to the first and second mounting members. Accordingly, the housing portion is likely to be subjected to vibration or oscillation having relatively large amplitude, thus effectively inducing the bouncing displacement of the independent mass member and assuring increased impact of the independent mass member against the housing portion. Thus, the vibration-damping device of this mode exhibits a desired effect for limiting or restricting the surging of the elastic body, on the basis of the impact of the independent mass member against the housing portion with high efficiency.
(3) A vibration-damping device according to the above-indicated mode (1) or (2), wherein the housing portion includes a rigid case member bonded by vulcanization to the elastic body. In the vibration-damping device of this mode of the invention, the rigid case member functions to prevent or limit deformation of a profile of the inner surface of the housing portion, when the elastic body undergoes elastic deformation due to a static and an active load applied to the vibration-damping device. That is, the use of the case member is effective to stabilize a desired spacing distance between abutting surfaces of the independent mass member and the housing portion, and amplitude of displacement of the independent mass member relative to the housing portion. Thus, the vibration-damping device of this mode of the invention is capable of exhibiting a desired surging limiting effect with respect to the elastic body thereof, on the basis of the impact of the independent mass member against the housing portion, with high stability.
(4) A vibration-damping device according to the above-indicated mode (3), wherein the case member includes an abutting surface adapted to impact against the independent mass member, and the abutting surface of the case member is covered by an abutting rubber layer integrally formed with the elastic body. The vibration-damping device constructed according to this mode of the invention makes it possible to eliminate or minimize impact noises generated upon impact of the independent mass member against the case member, while permitting the use of an independent mass member which is made of a rigid material such as metal and which is naked without being covered with an elastic layer. Since the abutting rubber layer is formed integrally with the elastic body, the abutting rubber layer is produced with high efficiency.
(5) A vibration-damping device according to any one of the above-indicated modes (1)-(4), wherein the connecting portion of the elastic body undergoes shear deformation thereof upon application of a vibrational load between said first and second mounting members, and the independent mass member is independently displaceable relative to and is brought into impact against the housing portion in a direction in which the connecting portion of the elastic body undergoes shear deformation. In the vibration-damping device according to this mode of the invention, the independent mass member is brought into impact against the housing portion in the direction in which the connecting portion of the elastic body undergoes the shear deformation, so that the housing portion is elastically displaced or oscillated with relatively large amplitude. Therefore, the vibration-damping device of this mode is capable of exhibiting a high surging limiting effect with respect to its elastic body, on the basis of the impact (abutting contact) of the independent mass member against the housing portion, thus effectively preventing the vibration-damping device suffering from deterioration of its vibration damping capability due to the surging of the elastic body thereof.
(6) A vibration-damping device according to the above-indicated mode (5), wherein the housing portion formed in the connecting portion of the elastic body is located at an intermediate portion between the first and second mounting members, and extends in a direction perpendicular to the direction in which the connecting portion of the elastic body undergoes shear deformation. This arrangement enables to obtain a sufficient volume of the housing portion, thus making it possible to obtain a sufficient volume of the independent mass member to be accommodated in the housing portion. Accordingly, the vibration-damping device of this mode can exhibit effectively the surging limiting effect with respect to its elastic body, on the basis of the impact (abutting contact) of the independent mass member against the housing portion.
(7) A vibration-damping device according to the above-indicated mode (6), wherein the independent mass member has an elongated shape and extends continuously in a longitudinal direction of the housing portion. This arrangement permits that the independent mass member is able to have a mass as much as possible within a predetermined amount of volume of the housing portion, thus assuring an enhanced surging limiting effect of the vibration-damping device on the basis of the impact of the independent mass member against the housing portion, with the housing portion made in compact in size.
(8) A vibration-damping device according to any one of the above-indicated modes (1)-(7), wherein the first mounting member comprises an inner shaft member and the second mounting member comprises an outer sleeve member disposed radially outward of the inner shaft member with a radial spacing therebetween, while the elastic body is interposed between the inner shaft member and the outer sleeve member. The elastic body has a pair of voids formed therethrough over an entire axial length thereof at respective portions opposed to each other in a diametric direction perpendicular to an axis of the inner shaft member in which a vibrational load is applied between the inner shaft member and said outer sleeve member, to thereby provide a pair of elastic connecting portions of the elastic body. The pair of elastic connecting portions elastically connect the inner shaft member and the outer sleeve member with each other in respective diametric directions perpendicular to the axis of the inner shaft member, and the housing portion being formed in each of the pair of the elastic connecting portions of the elastic body.
The vibration-damping device constructed according to the mode (8) of the invention ensures an increased ratio of the spring constants of the elastic body in the two mutually perpendicular diametric directions, namely, a first diametric direction in which the pair of voids are opposed to each other and a second diametric direction which is perpendicular to the first diametric direction. This leads to a high degree of freedom in tuning the spring characteristics of the vibration-damping device. Therefore, the vibration-damping device of this mode of the invention is suitably applicable to a suspension bushing or an engine mount for automotive vehicles. Moreover, the surging of the elastic body generated upon application of the specific-frequency vibration between the inner shaft member and the outer sleeve member is effectively limited on the basis of the impact of the independent mass members against the respective housing portions. That is, the above-indicated arrangement of the mode (8) of the invention makes it possible to provide a cylindrical elastic mount which is simple in construction and which is capable of exhibiting an excellent vibration damping effect with respect to input vibrations over a wide frequency range.
(9) A vibration-damping device according to the above-indicated mode (8), wherein each of the pair of elastic connecting portions has a through hole axially extending therethrough to thereby constitute the housing portion, while the independent mass member has a rod shape and is disposed in the respective through hole of each of the pair of the elastic connecting portions such that the independent mass member extends through the through hole and is provided with a projection for preventing a disengagement thereof from the through hole. This arrangement facilitates the impact of the independent mass member against the housing portion with high efficiency, during the surging of the elastic body in which the elastic body is likely to undergo shearing deformation with relatively large amplitude. The arrangement of the mode (9) makes it possible to provide effectively an elastic cylindrical mount which is capable of eliminating or reducing the deterioration of the vibration damping capability thereof due to the surging of the elastic body, while exhibiting an excellent vibration damping effect with respect to vibrations over a wide frequency range with high stability.
(10) A vibration-damping device according to any one of the above-indicated modes (1)-(9), wherein the second mounting member has a cylindrical portion, and the first mounting member is substantially coaxially disposed on one of axially opposite sides of the cylindrical portion of the second mounting member with an axial spacing therebetween, while the elastic body has a substantially tapered cylindrical shape and extends radially outwardly from the first mounting member to an open end portion of the cylindrical portion of the second mounting member so as to elastically connect the first mounting member and the cylindrical portion of the second mounting member. The open end portion of the cylindrical portion of the second mounting member is fluid-tightly closed by the elastic body to thereby form within the cylindrical portion of the second mounting member a fluid chamber partially defined by the elastic body and filled with a non-compressible fluid, so that the vibration-damping device exhibit a vibration damping effect on the basis of flows of the non-compressible fluid. The housing portion formed in the connecting portion of the elastic body is located at an intermediate portion between the first and second mounting members in a direction in which the first mounting member and the cylindrical portion of the second mounting member are connected to each other via the connecting portion, and extends in a circumferential direction of the elastic body.
The vibration-damping device constructed according to this mode (10) of the invention is able to exhibit an excellent elastic support capacity and an excellent vibration damping characteristics with respect to a vibrational load applied in an axial direction of the second mounting member in which the first and second mounting members are moved toward each other. For this reason, the vibration-damping device of this mode is suitably applicable to an engine mount for an automotive vehicle, for example. Further, the surging of the elastic body upon application of the vibrational load between the first and second mounting members is effectively limited on the basis of the impact of the independent mass member against the housing portion. Therefore, this arrangement of the mode of the invention enables to provide a non-cylindrical vibration-damping device which is simple in construction and which is capable of exhibiting an excellent vibration damping effect with respect to input vibrations over a wide frequency range.
(11) A vibration-damping device according to any one of the above-indicated mode (1)-(10) of the invention, wherein the housing portion includes a housing body member fixed to the elastic body and being open at an opening thereof in an surface of the elastic body, and a covering member adapted to cover the opening of the housing body member, while the independent mass member is accommodated within the housing body member whose opening is closed by the covering member fixed thereto. This arrangement of the mode (11) of the invention enables to easily manufacture a non-cylindrical vibration-damping device which is capable of exhibiting an excellent vibration-damping device with respect to vibrations whose frequencies correspond to the surging frequency of the elastic body.
In order to assure a desired surging limiting effect of a vibration-damping device according to the present invention, and a reduced impact noise upon impact of the independent mass member against the housing portion, at least one of abutting surfaces of the independent mass member and the housing portion may preferably have a Shore D hardness of 80 or lower, more preferably, within a range of 20-40, as measured in accordance with ASTM method D-2240.
For the above-mentioned improved surging limiting effect and the reduced impact noise, at least one of the abutting surfaces of the independent mass member and the housing portion is also arranged to have a modulus of elasticity within a range of 1-104 MPa, more preferably, 1-103 MPa, and a loss tangent is not less than 10-3, more preferably within a range of 0.01-10, preferably.
Preferably, the independent mass member in its single form has a mass within a range of 10-1000 g, more preferably within a range of 50-500 g. Namely, if the mass of the independent mass member is set to 1000 g or smaller, more preferably 500 g or smaller, the independent mass member is likely to excite its bouncing displacement upon elastic displacement of the elastic body. If the mass of the independent mass member is set to 10 g or more, more preferably 50 g or more, the vibration-damping device is able to effectively exhibit a desired surging limiting effect on the basis of the impact of the independent mass member against the housing portion. It should be appreciated that when the vibration-damping device includes a plurality of independent mass members, each of the plurality of independent mass members is preferably arranged to have a mass held within the above-indicated preferred range.
For ensuring an excellent surging limiting or vibration damping effect of the vibration-damping device of this invention, a spacing between the abutting surfaces of the independent mass member and the housing portion is preferably arranged such that the independent mass member is reciprocatory movable relative to the housing portion by a distance of 0.2-1.6 mm, more preferably 0.2-1.0 mm, in a direction in which a vibrational load is applied to the housing portion.